A control strategy for converters of wind generator under unbalanced grid voltage

By studying the behavior of wind generator under unbalanced grid voltage, it is shown that if no special control efforts are used, the behavior of wind generator under unbalanced grid voltage is deteriorated, mainly in the non-sinusoidal current and electromagnetic torque oscillations. To solve these problems, this paper presents a new control strategy that converters of wind generator under unbalanced grid voltage are controlled by direct power control techniques. These phenomena of the non-sinusoidal current and electromagnetic torque oscillations are analyzed theoretically according to the change of the active and reactive power of the stator of wind generator and the grid-side converter. In order to achieve sinusoidal stator currents and eliminate torque oscillations, the analysis provides the main ideas for generation of the active and reactive power references for the rotor-side converter and the grid-side converter, controlled by means of direct power control techniques. This paper presents a new algorithm that generates the rotor-side converter power references, without the necessity of sequence component calculations. The grid-side converter power references are provided by current and voltage sequence calculations. Both theoretical deduction and experimental results demonstrate the correctness and effectiveness of the proposed control strategy.